Solvent-based refinish coating compositions are known, and generally include a crosslinkable component and a crosslinking component. The crosslinking component causes the crosslinkable component to form crosslinks when the two are mixed. The crosslinkable component and the crosslinking component are kept separated in packs and then mixed just prior to being applied. This coating process shall be referred to herein as a “two-pack” coating composition process. The two pack coating process is known to produce coatings of very good quality.
One problem associated with such coating compositions is the relatively long time required to cure these compositions. Long cure times for automotive coatings can reduce productivity in automotive refinish shops by requiring the automobile to remain in the area in which it was spray coated for a longer period of time. Long cure times are also undesirable because they create longer waiting periods before a coating that can be readily sanded or buffed without fouling sandpaper. Longer cure times also prevent the practitioner from quickly removing coated automobile or truck bodies out of the spray booths to fully cure at other convenient locations. As a result, productivity of coating autobodies is decreased.
Attempts have been made to decrease the curing time of these two pack-coating compositions by using more reactive components or catalysts. However, while the use of such components decreases curing time, the higher reactivity of such components usually reduces the time to gelation, that is, reduces the pot life of the coating composition as well. In an extreme case, instant gelation of the composition can occur when the crosslinkable component, for example a polyisocyanate, is mixed with compounds or polymers having reactive amine groups. Thus, a need still exists for a two-pack coating composition that cures rapidly while still having a pot life that is acceptable to the automotive coatings industry.
U.S. Pat. Nos. 6,362,059 and 6,471,185—both to DuPont—disclose a dual cure resin system, wherein the functionality is provided by separate components, comprising in the range of from 0.5 to 8.0 weight percent, based on the weight of the binder component solids of secondary amine moieties and also comprising in the range of from 5.0 to 70 weight percent, based on the weight of the binder component solids of hydroxyl moieties. The resin system cures rapidly in a first stage to produce a coating surface that can be readily buffed or sanded and, thereafter, a second stage cure takes place over a period of days to produce a coating having more durable properties.